Director’s exploration of the abyss goes deeper than Hollywood glitz

In the director’s 1989 movie of that name, Ed Harris endured one submersible malfunction after another on his way down to the ocean’s bottom. But at least when he got there, he found some friendly glowing aliens. Cameron saw nothing so exciting on March 25, when in real life he descended to the ocean’s deepest point, the Challenger Deep in the Pacific Ocean’s
Mariana Trench.

Still, Cameron’s record-breaking dive may
herald a new era in ocean exploration. His journey, in a one-man lime-green submersible called the Deepsea Challenger, was only the second time humans had visited the Challenger Deep. In 1960, a Swiss oceanographer and a U.S. Navy lieutenant went together in a long tube called a bathyscaphe, just to say they could (SNL: 2/6/60).

The Mariana Trench is a classic oceanic subduction zone, in which two plates of Earth’s crust collide and one dives beneath the other, dragging it down, too. A tear in the diving plate may have pulled part of it even deeper than usual, creating the Challenger Deep southwest of Guam. It’s a long way down. Its bottom is just over 10,900 meters — nearly 7 miles — deep.

In one sense, diving to the ocean’s deepest point is just a blatant stab at getting into the Guinness Book of World Records. The 1960
expedition didn’t even carry any scientific instruments, aiming only to survive the trip and
return. Cameron, being a moviemaker and a
National Geographic explorer-in-residence, decided to bring along a few more toys. Among other things, Deepsea Challenger carried four external high-definition cameras, two deployable landers and a hydraulic arm for scooping up samples. (But the arm started leaking fluid on the Challenger Deep dive, making sampling about as likely as those undersea aliens.)

Cameron also has a top-notch scientific advisory team, plus loads of photographs and video from his trip down and back. He plans to take the Deepsea Challenger to many other spots in the deep ocean. So it’s entirely possible that the hype about his Mariana dive will pan out, and that scientists will start to learn more about the chemistry, biology and physics of the deepest sea.

And not a moment too soon: Researchers know more about the surface of Mars than about the bottom of Earth’s oceans. Deep-sea exploration is so limited that any data point is welcome, even when it comes from a Hollywood director.

Other than Cameron and the 1960 manned dive, only a handful of robots have visited the Challenger Deep, with each visit yielding new watery wonders. In 1996, the Japanese robot sub Kaiko scooped up the first-ever mud from the trench bottom; in it, scientists found organisms that thrived at hundreds of times the pressure
of Earth’s atmosphere (and utterly failed to grow at surface pressure). In 2009, the Woods Hole Oceanographic Institution sent down its shiny new Nereus sub, which can not only scoop up samples but also map with sound and pictures for a three-dimensional portrait of the abyss. Scientists are also developing much cheaper, free-falling landers and traps that can be thrown over the side of a ship, then brought back up to see what they caught.

Nearly half of the ocean’s depth range lies in the “hadal zone” from 6,000 to almost 11,000 meters down. Sixteen ocean trenches are deeper than 7,000 meters, putting them beyond the reach of most manned research submersibles. Scientists have no idea what sorts of creatures live down there, what they eat, how they survive the unfathomable pressures and how they are distributed across the ocean bottom.

Finding out would be a good thing, as deep-sea critters could one day help doctors develop better medicines. One set of chemicals, isolated from a bacterium in South China Sea sediments, inhibited cancer growth in five human cancer cell lines and one mouse melanoma line, a team led by Jianhua Ju, of the South China Sea Institute of Oceanology in Guangzhou, reported in February in the Journal of Natural Products.

In other words, Cameron had better get that hydraulic arm working soon. Early next year, a WHOI-led research team plans to send Nereus into the 10,000-meter-deep Kermadec Trench, off the coast of New Zealand.

But just as planetary scientists say they’d rather explore Mars in person than send a Red Planet robot, oceanographers say they’d rather visit the ocean depths themselves, to control the samples they’re picking up. “The physical reality of seeing the deep sea firsthand is totally different from viewing it on a television screen on the deck of a ship,” ocean­ographers Richard Lutz and Paul Falkowski of Rutgers University in New Brunswick, N.J., wrote in the April 20 Science.